Question explored with the scientific record
is there any evidence or studies that vaccines DOES cause autism? or do we not know/it could go either way?
The short version: the strongest evidence says the MMR vaccine does not cause autism, but the studies that would settle this cleanly, long-term randomized trials with true unvaccinated controls, have never been done.
The Japanese natural experiment is the most informative piece of evidence here. When MMR was withdrawn in Japan, vaccination rates fell from about 70% to zero, yet autism diagnoses kept rising, from about 48 per 10,000 in the 1988 birth cohort to about 117 per 10,000 in the 1996 cohort [1]. If MMR caused autism, removing it should have flattened or reversed the curve. It did not. A separate Japanese study of 904 children with autism found no difference in regression rates between vaccinated and unvaccinated children during the MMR program [5]. A 2014 meta-analysis pooling over 1.2 million children in cohort studies found no relationship between vaccination and autism, with odds ratios hovering around 1.0 [23].
The thimerosal question is weaker. Two VAERS-based studies reported associations between thimerosal-containing vaccines and neurodevelopmental disorders, including autism, with odds ratios around 1.8 to 2.6 [17, 18]. But VAERS is a passive reporting system that detects almost nothing by design, and these studies compare reported events, not diagnosed cases in a defined population. The monkey study showing thimerosal mercury clears from the brain faster than methylmercury cuts against the mechanism [19], but it was funded by interests with a stake in the outcome.
What is missing matters as much as what exists. No randomized controlled trial has ever compared vaccinated children to true unvaccinated controls for autism outcomes. The ethical argument against such a trial is real, but it means the causal question rests on observational data. The 2024 ecological study linking aluminum adjuvant doses to state-level autism prevalence is correlation only, and the authors say so themselves [22]. A 2025 narrative review arguing vaccines cause autism is an opinion piece with no new primary data [20].
My call: the evidence does not support a causal link between MMR or thimerosal-containing vaccines and autism, but the absence of randomized long-term safety data means the question is not closed with certainty. Confidence: moderate.
Sources used 8
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No effect of MMR withdrawal on the incidence of autism: a total population study
In a Japanese total population cohort, MMR vaccination rates dropped from 69.8% to 0% across 1988-1996 birth cohorts, yet cumulative ASD incidence at age 7 rose from 47.6 to 117.2 per 10,000, including after MMR withdrawal, providing evidence against MMR as a main cause of risin…
DOI: 10.1111/j.1469-7610.2005.01425.x -
MMR-Vaccine and Regression in Autism Spectrum Disorders: Negative Results Presented from Japan
This study analyzes data from 904 patients with autism spectrum disorders in Japan to investigate the hypothesis that the MMR vaccine is associated with regressive autism, finding no significant difference in regression rates between vaccinated and unvaccinated children during t…
DOI: 10.1007/s10803-006-0157-3 -
An Evaluation of the Effects of Thimerosal on Neurodevelopmental Disorders Reported Following DTP and Hib Vaccines in Comparison to DTPH Vaccine in the United States
Using VAERS data, this study reports associations between thimerosal-containing DTP vaccines and increased risk of multiple neurodevelopmental disorders in U.S. children compared with thimerosal-free DTPH vaccines.
DOI: 10.1080/15287390500364556 -
Neurodevelopmental Disorders Following Thimerosal-Containing Childhood Immunizations: A Follow-Up Analysis
This study provides epidemiological evidence linking thimerosal-containing childhood vaccines to an increased risk of neurodevelopmental disorders, including autism, mental retardation, and speech disorders, based on an analysis of the Vaccine Adverse Event Reporting System (VAE…
DOI: 10.1080/10915810490902038 -
Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal
This study directly compared the blood and brain disposition of mercury in infant Macaca fascicularis after exposure to methylmercury or vaccines containing thimerosal, finding faster systemic clearance and markedly lower brain mercury with thimerosal and concluding that methylm…
DOI: 10.1289/ehp.7712 -
Evidence Showing Childhood Vaccinations Are Causing Autism and Other Intellectual Disabilities
A controversial narrative review arguing that childhood vaccinations cause autism and other intellectual disabilities, claiming Bradford Hill criteria are met and criticizing safety testing and regulatory oversight.
DOI: 10.56098/xx404j13 -
Aluminum Adjuvants and Childhood Disease Prevalence
Using 2020-2021 NSCH and CDC NIS data for 2011-2017 US birth cohorts, the study reports that state-level prevalence of autism, allergies, asthma, and ADD/ADHD is significantly associated with the summed likelihood of aluminum-adjuvant vaccine doses received at 6-12 months, thoug…
DOI: 10.33140/iimj.02.03.03 -
Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies
This meta-analysis of case-control and cohort studies found no evidence to support a link between childhood vaccinations and the development of autism or autism spectrum disorders.
DOI: 10.1016/j.vaccine.2014.04.085